1. Field of the Invention
The present invention relates to a video signal processing integrated circuit.
2. Description of the Related Art
When displaying a television screen, the interlaced scan is usually performed and, for example, as shown in FIG. 6, a screen of one frame is displayed by scanning one frame twice separately for an odd field and an even field. Specifically, in the interlaced scan, all the scan lines of the odd field are line-by-line scanned from the top to the bottom of the television screen. After the scanning of the odd field, all the scan lines of the even field are scanned from the top to the bottom of the television screen such that the gaps of all the scan lines of the odd field are filled in. By repeating such scanning of the odd field and the even field, a television screen is displayed.
Each time the horizontal scan from left to right is completed for one scan line in each field, the horizontal scan position is require to be moved from right to left to start the horizontal scan for the next scan line. Such a line for moving the horizontal scan position within the field is referred to as a “horizontal retrace line”, and a time set for this horizontal retrace line is referred to as a “horizontal blanking interval”. When scanning from a present scan field to a next scan field, the vertical scan position must also be moved from bottom to top. Such a line for moving the vertical scan position between the fields is referred to as a “vertical retrace line”, and a time set for this vertical retrace line is referred to as a “vertical blanking interval (VBI)”. Since the vertical blanking interval is an interval caused based on a physical requirement for returning an electron beam from bottom to top of the television screen, for example, in the case of cathode-ray tubes; and is meaningless in terms of signal transmission, the interval is utilized for the teletext (character multiplex broadcast), EPG (Electronic Program Guide), etc.
The teletext is a system that displays additional characters and graphics in addition to normal video display: by transmitting a signal of encoded characters and graphics (hereinafter referred to as teletext signal) superimposed within the vertical blanking interval of a video signal on a transmitting side; and by extracting and decoding the teletext signal from the received video signal on a receiving side. For example, the teletext is employed in the closed caption (closed caption broadcasting) for displaying the concomitantly sent additional information in television programs as a caption on the television screen.
The EPG is a system that displays the EPG in addition to normal video display: by transmitting a signal of encoded television program listing (hereinafter referred to as EPG signal) superimposed within the vertical blanking interval of a video signal on the transmitting side; and by extracting and decoding the EPG signal from the received video signal on the receiving side. For example, the EPG is used in conjunction with a recording reservation function of a DVD recorder connected to a television receiver.
FIG. 7 depicts an outline of a format of a video signal with video additional data such as a teletext signal and EPG signal superimposed in the vertical blanking interval. Within the vertical blanking interval, equalizing pulses, vertical synchronization pulses, and equalizing pulses are arranged in this order, and the video additional data are superimposed as a portion of VBI data (data transmitted with the use of VBI) after the arrangement. The vertical synchronization signal is a signal for identifying the start of the vertical blanking interval. The vertical synchronization pulses are pulses inserted for every field. The equalizing pulses are pulses for equalization disposed before and after the vertical synchronization pulses to separate the vertical synchronization pulses of each field.
FIG. 8 depicts a format of a video signal representing the superimposed portion of VBI data as shown in a dash-line portion of FIG. 7. In the superimposed portion of VBI data, a horizontal synchronization signal, a color burst signal, and VBI data are arranged in this order, and the VBI data are made up of a clock run-in, a flaming code, and video additional data. The horizontal synchronization signal is a signal for identifying the start of each line in the field and has a waveform falling from 0-level to synchronization level, maintaining the synchronization level for a predetermined period, and returning from the synchronization level to the 0-level. The color burst signal is a color synchronization signal for color reproduction and has a waveform oscillating relative to the 0-level. The clock run-in is a reference clock string for dividing periods of bit data of the video signal and has a pulse-train-shaped waveform oscillating between the 0-level and 1-level. The flaming code is code information for dividing the periods of the minimum byte of the video signal and has a pulse-train-shaped waveform oscillating between the 0-level and 1-level.
A video signal processing integrated circuit 100 processing the video signal with the VBI data superimposed as above is provided with a VBI data slicer 110 as shown in FIG. 9 (see, e.g., Japanese Patent Application Laid-Open Publication No. Hei 6-178318). In FIG. 9, for convenience of description, a configuration other than the signal processing system of the VBI data is omitted.
As shown in FIG. 9, the VBI data slicer 110 is configured using a comparator 112, for example. The VBI data slicer 110 compares a video signal having a DC voltage adjusted by a clamp circuit 102 with a slice level VR to generate binarized VBI data of 0 or 1. A VBI data processing circuit 116 detects the clock run-in, the flaming code, and the video additional data based on the binarized VBI data generated by the VBI data slicer 110. The video additional data are divided into code data in units of byte by the clock run-in and the flaming code to be stored in a buffer memory 114. When the video additional data of one frame are stored in the buffer memory 114, the VBI data processing circuit 116 reads the video additional data of one frame stored in the buffer memory 114 to be supplied to the data to an RGB driver 118. As a result of this, there is generated the video additional data (characters, images, or EPG) displayed in addition to video on the television screen.
When conducting a shipment test of the video signal processing integrated circuit 100 equipped with the VBI data slicer 110, etc., a test signal generator generating an analog test signal compliant with the VBI data format is required to be prepared for a purpose such as detecting whether the VBI data slicer 110 can properly binarize the VBI data. However, the test signal generators are generally expensive and are unsuitable for the shipment test of mass-produced items since the reduction of test costs has recently been demanded. The shipment test, etc., are conducted based on a result of an operation of the VBI data slicer 110, etc., with an analog test signal from the test signal generator. Therefore, the shipment test may be conducted based on an unstable analog test signal due to external noises, etc., which may result in reducing yields.